Cells, Packs, … finally a Battery

Cells, Packs, … finally a Battery

I finally have the first modular instalment of my battery complete: 70 cells in a 7s10p configuration made of seven “packs”. The pack construction has been a bit slow, but along the way I’ve built some construction jigs and optimised the process. I think I could do the next set of packs in less than half the time!

First stage of the battery wired up and ready to go. It is almost exactly 0.5 kWh in capacity.

These are only half packs, because my design is to have 20-cell packs as the basic battery building block. This means that they don’t “stand up” as intended in the final design – but I don’t have the battery rack built yet anyway, so I’m happy for them to lay flat on their sides for now.

The battery looks great from every angle.

In place of a proper battery management system (BMS) I’m using a hobby charger that can do a balance charge (monitor the voltage of each of the 7 packs individually). This is why each “join” jumper between the packs needs to have a separate return wire.

Cheap inverter for now, but it powered the lights fine for this photo!

In keeping with the “start cheap and grow” philosophy of this project, I picked up a second-hand 24 V inverter for $50. It has a rated output of 600W, but is a modified sine wave inverter which is not great for  sensitive loads. As a proof of principle I used the 240 V power from the inverter to power the lights for these photos. With my current battery size I can’t even use the full 600 W as it would draw more than 2 A per cell (I’ve designed and tested for 1 A max).

It was a great feeling to finish the wiring harness and hit that switch. There’s a long way to go before the battery is really useful, but it is now ready to power things and let me move into a fun new stage of testing and design. I can return to cell extraction, and while I’m accumulating the next 70 good cells I can tackle the next big challenge: charging this battery from the sun!


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